Segment types in video coding

ABSTRACT

A method of and an apparatus for decoding a coded picture of a coded video sequence including a first segment and a second segment, are provided. The method includes determining a first decoding process for decoding the first segment, in which a first prediction is disallowed, based on at least a first syntax element of a high level syntax structure applicable to the first segment and the second segment, the first syntax element indicating that the first prediction is disallowed, and determining a second decoding process for decoding the second segment, in which a second prediction different than the first prediction is disallowed, based on at least a second syntax element of the high level syntax structure, the second syntax element indicating that the second prediction is disallowed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. patent application Ser. No.16/202,949 filed on Nov. 28, 2018, in the United States Patent andTrademark Office, which claims priority from U.S. Provisional PatentApplication No. 62/727,381, filed on Sep. 5, 2018, in the United StatesPatent and Trademark Office, which is incorporated herein by referencein its entirety.

BACKGROUND 1. Field

Methods and apparatuses consistent with embodiments relate to videoprocessing, and more particularly, segment types in video coding.

2. Description of Related Art

Video coding and decoding using inter-picture prediction with motioncompensation has been known for decades. Uncompressed digital video canconsist of a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate) of, for example, 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GByte of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in an input video signal, through compression. Compressioncan help reduce aforementioned bandwidth or storage space requirements,in some cases by two orders of magnitude or more. Both lossless andlossy compression, as well as a combination thereof, can be employed.Lossless compression refers to techniques where an exact copy of anoriginal signal can be reconstructed from a compressed original signal.When using lossy compression, a reconstructed signal may not beidentical to an original signal, but the distortion between the originaland reconstructed signals is small enough to make the reconstructedsignal useful for an intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision contribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding, some of which will be introducedbelow.

A coded video bitstream can be a compressed representation ofuncompressed source video and can be divided into coded pictures. Acoded picture comprises one or more picture segments. A picture segmentcan be, for example, a slice, a tile, a group of blocks (GOB), and soforth. Picture segments may include a segment header such as a sliceheader, a tile header, a GOB header, and so forth, that may includeinformation pertaining to one or more coding units (CUs) that can makeup a remainder of a segment. In some cases, information in the segmentheader can pertain to a first CU in the segment but can be overwrittenby corresponding update information located in CU headers. In othercases, the information in the segment header can pertain to all CUs inthe segment.

Picture segmentation was included in video compression technologies andstandards for a number of reasons. One reason for the introduction ofslices in MPEG-1 was the desire for Maximum Transfer Unit (MTU) sizematching. In a scenario in which a coded picture is larger than the MTUof a packet in a certain packet network, it was deemed desirable tosplit that picture into somewhat independently decodable units, hencethe introduction of slices. Another reason was the desire to simplifythe composition, perhaps in the compressed domain, of sub-pictures intoa coded picture. H.261's Group of Block (GOB) concept (and especiallythe GOB numbering used in H.261) is one early example of such atechnique, while H.263's rectangular slices are another example. Anotherreason was to enable encoding and/or decoding, in which multipleencoder/decoder processors or cores simultaneously decode parts of agiven picture.

Tiles are one more mechanism of several available in certain videocodecs that help to partition a coded video bitstream. A tile can be arectangular area of a picture. The scan order of CUs, also known asblocks or macroblocks, can be local to a tile, top left-to-right, thentop-to-bottom. A picture can be separated into a number of tiles whereineach CU can be part of exactly one tile. Tiles were introduced to enableparallel encoding and decoding, by allowing each processor or core tofocus its attention to only a part of the picture to be coded, in thatno communication to processors responsible for other tiles is requiredexcept for the final bitstream generation process; however, they canalso serve as a mechanism for picture composition.

Picture segmentation techniques can have in common that the segmentboundaries interrupt certain prediction mechanisms. For example, in somevideo coding technologies and standards, a segment boundary interruptsin-picture prediction mechanisms, such as motion vector prediction,intra prediction, and so forth. To what extent inter-picture predictionmechanisms, such as motion compensation using samples outside of thesegment boundary is allowed, depends on the video coding technology orstandard. For example, in H.263+, the independent segment decoding modeoffers a setting in which no import of sample values through motioncompensation across a segment boundary is allowed. Constrained tile setsin H.265 serve a similar purpose.

Picture segmentation techniques can further have in common that onlycertain types of coding units are allowed in a segment of a given type.For example, in some video coding technologies and standards, an intraslice can contain only CUs coded in intra mode, an inter slice cancontain CUs in intra and inter mode, and a bi-predicted slice cancontain CUs coded in intra, inter, and bi-predicted mode. As it can beobserved, in at least some video coding technologies or standards, thesegment types form a hierarchy, such as intra segments are the mostrestrictive, followed by inter segments, followed by bi-predictedsegments.

Intra segments can be used to reset the decoder state to a known statewith respect to certain part of the current decoded picture (covered bythe intra segment).

Recent video coding technologies can include techniques that sharecertain similarities between inter, intra, and (perhaps to a lesserextent) bi-prediction. For example, the screen content coding (SCC)profile of H.265 includes a technology known as intra block copy (IBC),which can be characterized as a motion compensation mechanism in whichthe reference sample information is part of the same decoded picture asthe samples under reconstruction. See, e.g., “HEVC Screen Content CodingDraft Text,” ITU-T/ISO/IEC, JCTVC-T1005, 2015. No previously decodedreference picture needs to be accessed, which is a feature that iscommon for intra coding. However, the reconstruction of a given CU canrequire sample information from outside the CU, which is a feature that,in older video coding standards such as MPEG-2, is traditionallyconsidered a feature of inter coding.

The interaction between intra segments and certain modern coding toolssuch as IBC can be complicated. On one hand, IBC has been shown, atleast in certain cases, as an effective tool to improve codingefficiency for intra codec areas of a picture under reconstruction.However, IBC in at least some cases works better the more area of thepicture under reconstruction is available for IBC's use as referencesamples, and that may include samples outside of the current segmentunder reconstruction. However, using samples outside the current segmentfor IBC reference can be counter-productive to the goal of intrasegments resetting a given area to a known state without referring toany information outside the segment.

The same can be true for arguably less advanced (or, at least, older)tools, such as intra prediction.

Accordingly, video compression technologies or standards tend to forbidany reference to outside sample and meta information by intra slice CUs.This can be implemented, for example, by marking any samples and any CUsoutside the segment boundary as unavailable for prediction. Thisdecision, however, in at least some cases in which the goal of intrasegments of resetting the decoding process is irrelevant, unnecessarilyreduces the coding efficiency.

SUMMARY

According to embodiments, a method of decoding a coded picture of acoded video sequence including a first segment and a second segment, isperformed by at least one processor and includes determining a firstdecoding process for decoding the first segment, in which a firstprediction is disallowed, based on at least a first syntax element of ahigh level syntax structure applicable to the first segment and thesecond segment, the first syntax element indicating that the firstprediction is disallowed. The method further includes determining asecond decoding process for decoding the second segment, in which asecond prediction different than the first prediction is disallowed,based on at least a second syntax element of the high level syntaxstructure, the second syntax element indicating that the secondprediction is disallowed. The method further includes decoding the firstsegment, based on the first decoding process in which the firstprediction is disallowed, and decoding the second segment, based on thesecond decoding process in which the second prediction is disallowed.

According to embodiments, an apparatus for decoding a coded picture of acoded video sequence including a first segment and a second segment,includes at least one memory configured to store computer program code,and at least one processor configured to access the at least one memoryand operate according to the computer program code. The computer programcode includes first determining code configured to cause the at leastone processor to determine a first decoding process for decoding thefirst segment, in which a first prediction is disallowed, based on atleast a first syntax element of a high level syntax structure applicableto the first segment and the second segment, the first syntax elementindicating that the first prediction is disallowed. The computer programcode further includes second determining code configured to cause the atleast one processor to determine a second decoding process for decodingthe second segment, in which a second prediction different than thefirst prediction is disallowed, based on at least a second syntaxelement of the high level syntax structure, the second syntax elementindicating that the second prediction is disallowed. The computerprogram code further includes first decoding code configured to causethe at least one processor to decode the first segment, based on thefirst decoding process in which the first prediction is disallowed, andsecond decoding code configured to cause the at least one processor todecode the second segment, based on the second decoding process in whichthe second prediction is disallowed.

According to embodiments, a non-transitory computer-readable storagemedium stores a program for decoding a coded picture of a coded videosequence including a first segment and a second segment. The programincludes instructions that cause a processor to determine a firstdecoding process for decoding the first segment, in which a firstprediction is disallowed, based on at least a first syntax element of ahigh level syntax structure applicable to the first segment and thesecond segment, the first syntax element indicating that the firstprediction is disallowed. The instructions further cause the processorto determine a second decoding process for decoding the second segment,in which a second prediction different than the first prediction isdisallowed, based on at least a second syntax element of the high levelsyntax structure, the second syntax element indicating that the secondprediction is disallowed. The instructions further cause the processorto decode the first segment, based on the first decoding process inwhich the first prediction is disallowed, and decode the second segment,based on the second decoding process in which the second prediction isdisallowed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of a communication system accordingto an embodiment.

FIG. 2 is a diagram of a placement of a video encoder and a videodecoder in a streaming environment, according to an embodiment.

FIG. 3 is a functional block diagram of a video decoder according to anembodiment.

FIG. 4 is a functional block diagram of a video encoder according to anembodiment.

FIG. 5 is a diagram of a tiled picture according to an embodiment.

FIGS. 6A and 6B are diagrams of parallel decoder systems for segmentedpictures, according to an embodiment.

FIG. 7 is a diagram of syntax and semantics of an IP slice syntaxelement, according to an embodiment.

FIG. 8 is a diagram of syntax and semantics of a PI slice syntaxelement, according to an embodiment.

FIG. 9 is a diagram of syntax and semantics of a B slice syntax element,according to an embodiment.

FIG. 10 is a diagram of syntax and semantics of a BI, PI, and IP slicesyntax element, according to an embodiment.

FIG. 11 is a diagram of syntax and semantics of prediction acrossboundaries flags, according to an embodiment.

FIG. 12 is a diagram of a computer system suitable for implementingembodiments.

FIG. 13 is a flowchart illustrating a method of decoding a coded pictureof a coded video sequence comprising a first segment and a secondsegment, according to an embodiment.

FIG. 14 is a simplified block diagram of an apparatus for decoding acoded picture of a coded video sequence comprising a first segment and asecond segment, according to an embodiment.

DETAILED DESCRIPTION

Embodiments relate to video coding and decoding, and more specifically,to a segmentation of a coded video picture into segments such as slicesand tiles that may not conform to known types of intra, inter,bi-predicted slices or tiles. For example, a slice or tile containingonly intra encoded blocks may still use prediction information fromslices or tiles outside the slice or tile under reconstruction, but ofthe same picture in a decoding order. In such a scenario, the picture,as a whole, may be decodable independently from other pictures, whereasthe slice or tile may require other slices or tiles of the same picturefor successful decoding.

FIG. 1 is a simplified block diagram of a communication system (100)according to an embodiment. The communication system (100) may includeat least two terminals (110-120) interconnected via a network (150). Forunidirectional transmission of data, a first terminal (110) may codevideo data at a local location for transmission to the other terminal(120) via the network (150). The second terminal (120) may receive thecoded video data of the other terminal from the network (150), decodethe coded data and display the recovered video data. Unidirectional datatransmission may be common in media serving applications and the like.

FIG. 1 illustrates a second pair of terminals (130, 140) provided tosupport bidirectional transmission of coded video that may occur, forexample, during videoconferencing. For bidirectional transmission ofdata, each terminal (130, 140) may code video data captured at a locallocation for transmission to the other terminal via the network (150).Each terminal (130, 140) also may receive the coded video datatransmitted by the other terminal, may decode the coded data and maydisplay the recovered video data at a local display device.

In FIG. 1, the terminals (110-140) may be illustrated as servers,personal computers and smart phones but the principles of embodimentsare not so limited. Embodiments find application with laptop computers,tablet computers, media players and/or dedicated video conferencingequipment. The network (150) represents any number of networks thatconvey coded video data among the terminals (110-140), including forexample wireline and/or wireless communication networks. Thecommunication network (150) may exchange data in circuit-switched and/orpacket-switched channels. Representative networks includetelecommunications networks, local area networks, wide area networksand/or the Internet. For the purposes of the present discussion, thearchitecture and topology of the network (150) may be immaterial to theoperation of embodiments unless explained herein below.

FIG. 2 is a diagram of a placement of a video encoder and a videodecoder in a streaming environment, according to an embodiment. Thedisclosed subject matter can be equally applicable to other videoenabled applications, including, for example, video conferencing,digital TV, storing of compressed video on digital media including CD,DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (213) that caninclude a video source (201), for example a digital camera, creating,for example, an uncompressed video sample stream (202). That samplestream (202), depicted as a bold line to emphasize a high data volumewhen compared to encoded video bitstreams, can be processed by anencoder (203) coupled to the camera (201). The encoder (203) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video bitstream (204), depicted as a thin line toemphasize the lower data volume when compared to the sample stream, canbe stored on a streaming server (205) for future use. One or morestreaming clients (206, 208) can access the streaming server (205) toretrieve copies (207, 209) of the encoded video bitstream (204). Aclient (206) can include a video decoder (210) which decodes theincoming copy of the encoded video bitstream (207) and creates anoutgoing video sample stream (211) that can be rendered on a display(212) or other rendering device (not depicted). In some streamingsystems, the video bitstreams (204, 207, 209) can be encoded accordingto certain video coding/compression standards. Examples of thosestandards include ITU-T Recommendation H.265. Under development is avideo coding standard informally known as Versatile Video Coding (VVC).The disclosed subject matter may be used in the context of VVC.

FIG. 3 is a functional block diagram of a video decoder (210) accordingto an embodiment.

A receiver (310) may receive one or more codec video sequences to bedecoded by the decoder (210); in the same or another embodiment, onecoded video sequence at a time, where the decoding of each coded videosequence is independent from other coded video sequences. The codedvideo sequence may be received from a channel (312), which may be ahardware/software link to a storage device which stores the encodedvideo data. The receiver (310) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (310) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (315) may be coupled inbetween receiver (310) and entropy decoder/parser (320) (“parser”henceforth). When receiver (310) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosychronous network, the buffer (315) may not be needed, or can besmall. For use on best effort packet networks such as the Internet, thebuffer (315) may be required, can be comparatively large and canadvantageously of adaptive size.

The video decoder (210) may include a parser (320) to reconstructsymbols (321) from the entropy coded video sequence. Categories of thosesymbols include information used to manage operation of the decoder(210), and potentially information to control a rendering device such asa display (212) that is not an integral part of the decoder but can becoupled to it, as was shown in FIG. 3. The control information for therendering device(s) may be in the form of Supplementary EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (320) mayparse/entropy-decode the coded video sequence received. The coding ofthe coded video sequence can be in accordance with a video codingtechnology or standard, and can follow principles well known to a personskilled in the art, including variable length coding, Huffman coding,arithmetic coding with or without context sensitivity, and so forth. Theparser (320) may extract from the coded video sequence, a set ofsubgroup parameters for at least one of the subgroups of pixels in thevideo decoder, based upon at least one parameters corresponding to thegroup. Subgroups can include Groups of Pictures (GOPs), pictures, tiles,slices, macroblocks, Coding Units (CUs), blocks, Transform Units (TUs),Prediction Units (PUs) and so forth. The entropy decoder/parser may alsoextract from the coded video sequence information such as transformcoefficients, quantizer parameter (QP) values, motion vectors, and soforth.

The parser (320) may perform entropy decoding/parsing operation on thevideo sequence received from the buffer (315), so to create symbols(321). The parser (320) may receive encoded data, and selectively decodeparticular symbols (321). Further, the parser (320) may determinewhether the particular symbols (321) are to be provided to a MotionCompensation Prediction unit (353), a scaler/inverse transform unit(351), an Intra Prediction unit (352), or a loop filter unit (354).

Reconstruction of the symbols (321) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (320). The flow of such subgroup control information between theparser (320) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, decoder (210) can beconceptually subdivided into a number of functional units as describedbelow. In a practical implementation operating under commercialconstraints, many of these units interact closely with each other andcan, at least partly, be integrated into each other. However, for thepurpose of describing the disclosed subject matter, the conceptualsubdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (351). Thescaler/inverse transform unit (351) receives quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (321) from the parser (320). It can output blockscomprising sample values, which can be input into aggregator (355).

In some cases, the output samples of the scaler/inverse transform (351)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (352). In some cases, the intra pictureprediction unit (352) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current (partly reconstructed) picture(356). The aggregator (355), in some cases, adds, on a per sample basis,the prediction information the intra prediction unit (352) has generatedto the output sample information as provided by the scaler/inversetransform unit (351).

In other cases, the output samples of the scaler/inverse transform unit(351) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a Motion Compensation Prediction unit (353) canaccess reference picture memory (357) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (321) pertaining to the block, these samples can beadded by the aggregator (355) to the output of the scaler/inversetransform unit (in this case called the residual samples or residualsignal) so to generate output sample information. The addresses withinthe reference picture memory form where the motion compensation unitfetches prediction samples can be controlled by motion vectors,available to the motion compensation unit in the form of symbols (321)that can have, for example X, Y, and reference picture components.Motion compensation also can include interpolation of sample values asfetched from the reference picture memory when sub-sample exact motionvectors are in use, motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (355) can be subject to variousloop filtering techniques in the loop filter unit (354). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video bitstream andmade available to the loop filter unit (354) as symbols (321) from theparser (320), but can also be responsive to meta-information obtainedduring the decoding of previous (in decoding order) parts of the codedpicture or coded video sequence, as well as responsive to previouslyreconstructed and loop-filtered sample values.

The output of the loop filter unit (354) can be a sample stream that canbe output to the render device (212) as well as stored in the referencepicture memory (356) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. Once a coded picture is fullyreconstructed and the coded picture has been identified as a referencepicture (by, for example, parser (320)), the current reference picture(356) can become part of the reference picture buffer (357), and a freshcurrent picture memory can be reallocated before commencing thereconstruction of the following coded picture.

The video decoder (210) may perform decoding operations according to apredetermined video compression technology that may be documented in astandard, such as ITU-T Rec. H.265. The coded video sequence may conformto a syntax specified by the video compression technology or standardbeing used, in the sense that it adheres to the syntax of the videocompression technology or standard, as specified in the videocompression technology document or standard and specifically in theprofiles document therein. Also necessary for compliance can be that thecomplexity of the coded video sequence is within bounds as defined bythe level of the video compression technology or standard. In somecases, levels restrict the maximum picture size, maximum frame rate,maximum reconstruction sample rate (measured in, for example megasamplesper second), maximum reference picture size, and so on. Limits set bylevels can, in some cases, be further restricted through HypotheticalReference Decoder (HRD) specifications and metadata for HRD buffermanagement signaled in the coded video sequence.

In an embodiment, the receiver (310) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (210) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal-to-noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 4 is a functional block diagram of a video encoder (203) accordingto an embodiment.

The encoder (203) may receive video samples from a video source (201)(that is not part of the encoder) that may capture video image(s) to becoded by the encoder (203).

The video source (201) may provide the source video sequence to be codedby the encoder (203) in the form of a digital video sample stream thatcan be of any suitable bit depth (for example: 8 bit, 10 bit, 12 bit, .. . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ) and anysuitable sampling structure (for example Y CrCb 4:2:0, Y CrCb 4:4:4). Ina media serving system, the video source (201) may be a storage devicestoring previously prepared video. In a videoconferencing system, thevideo source (201) may be a camera that captures local image informationas a video sequence. Video data may be provided as a plurality ofindividual pictures that impart motion when viewed in sequence. Thepictures themselves may be organized as a spatial array of pixels,wherein each pixel can comprise one or more samples depending on thesampling structure, color space, etc. in use. A person skilled in theart can readily understand the relationship between pixels and samples.The description below focuses on samples.

According to an embodiment, the encoder (203) may code and compress thepictures of the source video sequence into a coded video sequence (443)in real time or under any other time constraints as required by theapplication. Enforcing appropriate coding speed is one function ofController (450). Controller controls other functional units asdescribed below and is functionally coupled to these units. The couplingis not depicted for clarity. Parameters set by controller can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. A person skilled in the art can readily identify other functionsof controller (450) as they may pertain to video encoder (203) optimizedfor a certain system design.

Some video encoders operate in what a person skilled in the art readilyrecognizes as a “coding loop.” As an oversimplified description, acoding loop can consist of the encoding part of an encoder (430)(“source coder” henceforth) (responsible for creating symbols based onan input picture to be coded, and a reference picture(s)), and a (local)decoder (433) embedded in the encoder (203) that reconstructs thesymbols to create the sample data that a (remote) decoder also wouldcreate (as any compression between symbols and coded video bitstream islossless in the video compression technologies considered in thedisclosed subject matter). That reconstructed sample stream is input tothe reference picture memory (434). As the decoding of a symbol streamleads to bit-exact results independent of decoder location (local orremote), the reference picture buffer content is also bit exact betweenlocal encoder and remote encoder. In other words, the prediction part ofan encoder “sees” as reference picture samples exactly the same samplevalues as a decoder would “see” when using prediction during decoding.This fundamental principle of reference picture synchronicity (andresulting drift, if synchronicity cannot be maintained, for examplebecause of channel errors) is well known to a person skilled in the art.

The operation of the “local” decoder (433) can be the same as of a“remote” decoder (210), which has already been described in detail abovein conjunction with FIG. 3. Briefly referring also to FIG. 3, however,as symbols are available and en/decoding of symbols to a coded videosequence by entropy coder (445) and parser (320) can be lossless, theentropy decoding parts of decoder (210), including channel (312),receiver (310), buffer (315), and parser (320) may not be fullyimplemented in local decoder (433).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. The description of encodertechnologies can be abbreviated as they are the inverse of thecomprehensively described decoder technologies. Only in certain areas amore detail description is required and provided below.

As part of its operation, the source coder (430) may perform motioncompensated predictive coding, which codes an input frame predictivelywith reference to one or more previously-coded frames from the videosequence that were designated as “reference frames.” In this manner, thecoding engine (432) codes differences between pixel blocks of an inputframe and pixel blocks of reference frame(s) that may be selected asprediction reference(s) to the input frame.

The local video decoder (433) may decode coded video data of frames thatmay be designated as reference frames, based on symbols created by thesource coder (430). Operations of the coding engine (432) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 3), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (433) replicates decodingprocesses that may be performed by the video decoder on reference framesand may cause reconstructed reference frames to be stored in thereference picture cache (434). In this manner, the encoder (203) maystore copies of reconstructed reference frames locally that have commoncontent as the reconstructed reference frames that will be obtained by afar-end video decoder (absent transmission errors).

The predictor (435) may perform prediction searches for the codingengine (432). That is, for a new frame to be coded, the predictor (435)may search the reference picture memory (434) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(435) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (435), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (434).

The controller (450) may manage coding operations of the video coder(430), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (445). The entropy coder translatesthe symbols as generated by the various functional units into a codedvideo sequence, by loss-less compressing the symbols according totechnologies known to a person skilled in the art as, for exampleHuffman coding, variable length coding, arithmetic coding, and so forth.

The transmitter (440) may buffer the coded video sequence(s) as createdby the entropy coder (445) to prepare it for transmission via acommunication channel (460), which may be a hardware/software link to astorage device that may store the encoded video data. The transmitter(440) may merge coded video data from the video coder (430) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (450) may manage operation of the encoder (203). Duringcoding, the controller (450) may assign to each coded picture a certaincoded picture type, which may affect the coding techniques that may beapplied to the respective picture. For example, pictures often may beassigned as one of the following frame types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other frame in the sequence as a source of prediction.Some video codecs allow for different types of Intra pictures,including, for example Independent Decoder Refresh Pictures. A personskilled in the art is aware of those variants of I pictures and theirrespective applications and features.

A Predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A Bi-directionally Predictive Picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded non-predictively,via spatial prediction or via temporal prediction with reference to onepreviously coded reference pictures. Blocks of B pictures may be codednon-predictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video coder (203) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video coder (203) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (440) may transmit additional datawith the encoded video. The video coder (430) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, Supplementary EnhancementInformation (SEI) messages, Visual Usability Information (VUI) parameterset fragments, and so on.

In the following, the embodiments are described using tiles as anexample of coded picture segments. The embodiments can, in at least somecases, equally be applied to other segment types such as slices, GOBsand so forth.

FIG. 5 is a diagram of a tiled picture according to an embodiment.

Referring to FIG. 5, in an embodiment, a coded picture (501) may bedivided into three tile bitstreams (502, 504, 506), which represent in areconstructed picture (508), three spatial regions (509, 510, 511),respectively. In this example, each tile may use a tile header (503,505, 507). The example uses three tiles, but a person skilled in the artcan readily generalize the example into more or less than three tiles.Each tile can contain, in addition to its header, one or more codingunits CUs, that can be arranged in scan order. That is, for coding unitsin consecutive order in the tile's bitstream (502, 504, or 506), thearea covered by the coding unit is arranged such that the followingcoding unit is to the right and to the bottom of the previous codingunits, following in principle the scan order established by cathode raytube (CRT) rays. A person skilled in the art is readily familiar withscan order of coding units for coding units of both uniform anddiffering sizes.

According to known video coding technologies or standards, only certainforms of prediction are allowed across tile boundaries as shown in thespatial representation of the reconstructed picture (508). For example,H.265's tiles break all forms of prediction within a coded picture, beit prediction from meta-data (such as intra prediction modes, motionvectors, and so forth), or sample prediction (such as prediction samplesused in intra prediction, or sample data for IBC prediction). H.265'smotion-constrained tile sets further break the import of sample valuesthrough motion compensation from spatial areas in reference picturesoutside of the current tile set. In that, motion constrained tile setsare comparable to H.263's rectangular slices with independent segmentdecoding mode enabled.

These sets of constraints were historically defined after identifyingcertain (limited) application scenarios, in reaction to these scenariosand in response to certain hardware-implementation related constraints.However, the introduction of new coding tools, the ever growing desirefor additional coding efficiency, and the recognition of additionalapplication scenarios make more flexible definitions of the semantics oftile boundaries with respect to interruption of different forms ofprediction desirable.

FIGS. 6A and 6B are diagrams of parallel decoder systems for segmentedpictures, according to an embodiment.

Referring to FIG. 5 and FIG. 6A, a system (600 a) is shown, in which thethree spatial regions (509, 510, 511) each cover an area too large to bedecoded by a single decoder. In such a scenario, the system (600 a) maybe used, the system (600 a) including multiple sub-decoders that eachproduce a video sample stream representing the content of a single codedtile. The incoming, tiled coded video bitstream can be decomposed in thecompressed domain into coded sub-bistreams representing the threespatial regions (509, 510, 511) by a parser (602). When using a suitablesyntax, such as the syntax of, for example, H.265 with motionconstrained tile sets enabled, the decomposition can be a relativelylightweight process requiring little (if any) signal processing beyondbitstream parsing. The (comparatively) low bandwidth nature of thecompressed coded video bitstream (when compared to reconstructed samplestreams) is shown as a thin line. Three sub-decoders (603, 604, 605) mayreceive, through similarly low bandwidth communication links (606, 607,608) (also depicted as thin lines), bits of the coded sub bitstreamsthey are responsible for decoding and decode one region per decoder intoa reconstructed tile. The samples of the reconstructed tiles asgenerated by the three sub-decoders (603, 604, 605), may be delivered byhigh bandwidth links (609, 610, 611) to a stitcher (612). The stitcher(612) may aggregate the tiles into a single sample stream representingall reconstructed tiles in a single reconstructed picture stream (613).Sub-decoders (603, 604, 605) may, in this scenario, have nocommunication relationship with each other, may exchange only (minimal)control information, but do not communicate prediction information norsample information between each other. Therefore, no such communicationrelationship is depicted.

Based on above observations, a person skilled in the art can readilydevise a corresponding encoding system, which is therefore not depictednor described in more detail.

As in system (600 a), by definition, there is no communication ofprediction information between the sub-decoders (602, 603, 604) of thedecoding system (600 a), nor any such communication in a comparableencoder system, such a system is appropriate for independentsub-decoders or sub-encoders. However, it may also be appropriate forapplication scenarios where the decoder and/or encoder are notdistributed into sub-decoders/sub-encoders, but based on applicationneeds. For example, if it is known that the (in this example: three)spatial regions have no semantic relationship with each other, there islittle, if any chance that coding efficiency gains can be realizedthrough prediction across region/tile boundaries. Any import (in theform of artifacts) of sample information from a neighboring tile intothe tile under reconstruction should be avoided. For example, if aspatial region were containing content from a camera source whereas theother spatial regions contain content from other camera sources,artificial content, other projections in a 360 scenario, and so on, thecorrelation between the content of the various reasons may be small ornon-existence. Accordingly, there may be little or no advantage of usingprediction between those regions, even if using prediction may betechnically feasible by the system design. This scenario was one of thereasons for the inclusion of motion constrained tile sets into H.265.

FIG. 6B depicts a somewhat different system design (600 b). Once more,the system comprises a parser (602) that decomposes an incoming tiledcoded video bitstream into three sub-bitstreams (606, 607, 608) thatfeed into three sub-decoders (603, 604, 605). The sub-decoders eachcreate reconstructed tiles that are conveyed (609, 610, 611) to astitcher (612), which in turn creates the output reconstructed picturestream (613). However, in this design, a limited amount of informationcan be passed between the sub-decoders (603, 604, 605) over a suitablecommunication link (614) of medium bandwidth—perhaps not enough forconveying large amounts of sample information, but more than for minimalcontrol information (to be described in more detail below). The natureof the communication link can be a full mesh, a bus, shared memory, orany other appropriate communication technique. Depicted as a mediumbandwidth communication link (614) here is a bus that connects thesub-decoders (603, 604, 605).

A person skilled in the art can readily devise a corresponding encodingsystem.

The decoding system (600 b) may allow the use of certain types ofprediction across tile boundaries. Which type of prediction can be usedrelies largely on the available bandwidth of the medium bandwidthcommunication link (614).

In a first example, the link (614) may have sufficient bandwidth forsmall amounts of meta data, and very limited sample data (such as, forexample, a few sample values per coding unit (CU) to be decoded). Insuch a scenario, certain intra prediction mechanisms may be supportable,but intra block copy and motion compensation may not be supportable.This scenario was contemplated with H.265's motion constrained tilesets.

In a second example, the link (614) may have sufficient bandwidth formeta data and sample data associated with motion compensation from asingle reference picture in previous decoding order, but insufficientbandwidth or insufficient coordination ability to use intra block copy.This is the scenario that was envisioned with H.265's nonmotion-constraint (regular) tile sets. Intra block copy may be moreburdensome in some implementations compared to (past picture) motioncompensation because it can require quasi-concurrent access of, in manyimplementations, closely neighboring sample data in the current picturememory, which can lead to cache inefficiencies (especially if the cachedesign is not optimized for IBC). The coordination ability can pose aconceptual problem. If the reconstruction of a tile can require theaccess of other tiles in the same reconstructed picture, the decodingpipeline for a given tile may need to stall until the IBC-referencedsamples in the other tile become available. While the discussion herein,so far, has focused on tiles, with respect to this scenario it should benoted that if the segments were not tiles but slices that are decodedlinearly and in scan order, the above coordination problem does notexist, though the memory access problem may still be an issue in someimplementations.

In a third example, the link (614) may have sufficient bandwidth andcoordination ability for both P-picture style motion compensation andIBC. Such a scenario is currently not contemplated in the context ofH.265, but is the basis of the “IP Slice” concept, described below.

Finally, in a fourth example, the medium bitrate link (614) may havesufficient bitrate (and coordination ability) to support all forms ofprediction contemplated in the video technology or standard, including,for example, intra prediction, IBC, P-style and B-style interprediction. Some shared memory and multi-processor architectures allowfor such a fourth scenario. Here, no limitations of use prediction toolsacross tile (or, indeed, segment) boundaries may be required.

It must be noted that, while the above description may read as if therewere a hierarchy of prediction technologies that may or may not befeasible based on link (614) bandwidth and/or coordination ability, thatis not necessarily the case. As one trivial example, the memorybandwidth requirements for IBC are in a similar magnitude compared to Pprediction, whereas B prediction can require twice that bandwidth (andmulti-hypothesis prediction even more). However, the coordination aspectof IBC may prevent its use across tile boundaries even if the memorybandwidth of the system design may allow for bi-prediction ormulti-hypothesis prediction. Other architectural constraints may also bepresent.

It can be noted that the above example hard ware architectures may beused in combination. For example, it is well possible that a hard tilingaccording to system (600 a) may be required to split a very largepicture (8 k and above) into units of manageable size (for example, atthe time of writing, 4 k resolution is implementable under commerciallyreasonable constraints in both software and hardware encoders anddecoders). Within those hard tiles (of, in this example 4 k resolution),further tiling can be advantageous, and can be achieved through one ormore of the scenarios related to system (600 b).

Once more, attention must be drawn that the selection of used predictionmechanisms across tile boundaries (or, more general, segment boundaries)can be driven not only by hardware implementation constraints such asthe ones mentioned above, but also by application needs. In some cases,it can be advantageous to prevent one or more forms of prediction acrosstile and segment boundaries from an application and coding efficiencyviewpoint.

In the current video coding technologies and standards, the forms ofprediction that are being interrupted are inflexible, and, in mostcases, tied to concepts and syntax elements that serve differentpurposes. Using H.265 as an example (the list below is non-exhaustive):

-   -   IBC is allowed only when certain profiles are enabled, and no        prediction of IBC is allowed across slice/tile boundaries,        regardless of profile;    -   motion compensation is allowed only for P slices and B slices        (and independent of tiles) and across tile/slice boundaries        unless a motion-constrained tile set syntax element is set; and    -   intra prediction is not allowed to cross slice boundaries but        can cross tile boundaries.

Some of these constraints can be explained with the gradual involvementof H.265. For example, H.265 was added after the first version of H.265was published, and therefore needed to be placed (and its use signaled)through a profile. However, regardless of the history that made certaindesign choices necessary, the H.265 design does not allow certaincombinations of prediction mechanisms across certain segment boundaries.This shortcoming of H.265 and other current video coding technologiesand standards is addressed now.

Changing the support of certain prediction mechanisms across a segmentboundary in a video compression technology or standard can have twoimplications, which both may need to be considered.

The first implication can be the need for specifying the operation of adecoder when a certain prediction mechanism is in use, or when it isdisallowed and therefore not in use. In many video coding technologiesand standards, this can be done by appropriately defining the“availability” of reference samples or reference meta data, and aninferring mechanism that becomes used when an unallowed predictionacross a segment boundary were implied in the bitstream. Thosemechanisms are well known to a person skilled in the art and not furtherelaborated on herein.

The second implication can be that the allowed prediction tools acrosssegment boundaries need to be specified in the bitstream. Options forthis signaling mechanism are described below, in an order from a minimalchange compared to the signaling mechanisms available in H.265 to moreuniversal mechanisms.

Of the four examples of architectural constraints described above inconjunction with system (600 b), the third example (allowing both IBCand P-prediction) can be allowed by the introduction of one or moreadditional slice types.

FIG. 7 is a diagram of syntax and semantics of an IP slice syntaxelement, according to an embodiment.

In the same or another embodiment, a new slice type referred to hereinas IP slice is introduced. An IP slice can be signaled using anappropriate value for the slice_type syntax element (701) in theslice_segment_header( ) syntax structure (702), as shown in FIG. 7, withthe modified (relative to H.265) semantics (703) of slice_type.Modifications are shown using underscored text to indicate additions.The IP slice type can share all its properties with an I slice, exceptthat it allows IBC across its slice boundaries. In the same or anotherembodiment, an Independent Decoder Refresh picture (IDR picture) can becomposed of I and IP slices (704).

FIG. 8 is a diagram of syntax and semantics of a PI slice syntaxelement, according to an embodiment.

In the same or another embodiment, a new slice type referred to hereinas PI slice is introduced. A PI slice can be can be signaled using anappropriate value for the slice_type syntax element (701) in theslice_segment_header( ) syntax structure (702), as shown in FIG. 7 withthe modified semantics (801) of slice_type as shown in FIG. 8. The PIslice type shares all its properties with a P slice, except that itallows IBC across its slice boundaries.

FIG. 9 is a diagram of syntax and semantics of a B slice syntax element,according to an embodiment.

In the same or another embodiment, a new slice type referred to hereinas BI slice is introduced. A BI slice can be can be signaled using anappropriate value for the slice_type syntax element (701) in theslice_segment_header( ) syntax structure (702), as shown in FIG. 7, withthe modified semantics (901) of slice_type as shown in FIG. 9. The BIslice type shares all its properties with a B slice, except that itallows IBC across its slice boundaries.

FIG. 10 is a diagram of syntax and semantics of a BI, PI, and IP slicesyntax element, according to an embodiment.

In the same or another embodiment, two or more of the aforementionednovel slice types can be specified in combination. As an example, FIG.10 shows the semantics (1001) of the slice_type syntax element with allthree aforementioned novel slice types included.

In the same or another embodiment, the use of traditional I, B, and Pslices can imply that no IBC prediction is allowed across sliceboundaries, regardless of the profile in use.

FIG. 11 is a diagram of syntax and semantics of prediction acrossboundaries flags, according to an embodiment.

Referring to FIG. 11, in the same or another embodiment, a new syntaxelement ibc_accross_slice_boundaries_allowed_flag (1101) and/oribc_across_tile_boundaries_allowed_flag, can be introduced to a highlevel syntax structure such as, for example, slice segment header(1102), tile header, picture parameter set, sequence parameter set,picture header, GOP header, sequence header, or any other appropriatehigh level syntax structure. The semantics of such a flag can be asshown in FIG. 11, with ibc_accross_slice_boundaries_allowed_flag as anexample.

In the same or another embodiment, similar flags can be introduced forcertain other prediction tools, including but not limited to intraprediction (intra_pred_accross_slice_boundaries_allowed_flag, 1104),P-style motion compensation(p-prediction-across-slice-boundaries-allowed-flag, 1105), bi-predictedmotion compensation (b-prediction-across-slice-boundaries-allowed-flag,1106), and so forth. A person skilled in the art can readily devicesimilar syntax elements pertaining to the segment types such as tiles,GOBs, and so forth.

Many optimizations of the coding of aforementioned flag or flags can bepossible. For example, since bi-prediction, by definition, is allowedonly for B-slices, the presence ofb-prediction-across-slice-boundaries-allowed-flag could be gated uponthe slice type being a B-slice. Whether or not such parsing dependenciesare worth the coding efficiency is topic has that been addressed invideo coding technologies and standards in different, and sometimesinconsistent ways. Either form is meant to be included.

The techniques for prediction across segment boundaries, describedabove, can be implemented as computer software using computer-readableinstructions and physically stored in one or more computer-readablemedia.

FIG. 12 is a diagram of a computer system (1200) suitable forimplementing embodiments.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by computer central processing units (CPUs),Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 12 for computer system (1200) are examplesin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments. Neither should the configuration of components beinterpreted as having any dependency or requirement relating to any oneor combination of components illustrated in the embodiment of a computersystem (1200).

Computer system (1200) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1201), mouse (1202), trackpad (1203), touchscreen (1210), data-glove (1204), joystick (1205), microphone (1206),scanner (1207), camera (1208).

Computer system (1200) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1210), data-glove (1204), or joystick (1205), but therecan also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1209), headphones(not depicted)), visual output devices (such as screens (1210) toinclude cathode ray tube (CRT) screens, liquid-crystal display (LCD)screens, plasma screens, organic light-emitting diode (OLED) screens,each with or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1200) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1220) with CD/DVD or the like media (1221), thumb-drive (1222),removable hard drive or solid state drive (1223), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1200) can also include interface(s) to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include global systems for mobile communications(GSM), third generation (3G), fourth generation (4G), fifth generation(5G), Long-Term Evolution (LTE), and the like, TV wireline or wirelesswide area digital networks to include cable TV, satellite TV, andterrestrial broadcast TV, vehicular and industrial to include CANBus,and so forth. Certain networks commonly require external networkinterface adapters that attached to certain general purpose data portsor peripheral buses ((1249)) (such as, for example universal serial bus(USB) ports of the computer system (1200); others are commonlyintegrated into the core of the computer system (1200) by attachment toa system bus as described below (for example Ethernet interface into aPC computer system or cellular network interface into a smartphonecomputer system). Using any of these networks, computer system (1200)can communicate with other entities. Such communication can beuni-directional, receive only (for example, broadcast TV),uni-directional send-only (for example CANbus to certain CANbusdevices), or bi-directional, for example to other computer systems usinglocal or wide area digital networks. Certain protocols and protocolstacks can be used on each of those networks and network interfaces asdescribed above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1240) of thecomputer system (1200).

The core (1240) can include one or more Central Processing Units (CPU)(1241), Graphics Processing Units (GPU) (1242), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1243), hardware accelerators (1244) for certain tasks, and so forth.These devices, along with Read-only memory (ROM) (1245), Random-accessmemory (RAM) (1246), internal mass storage such as internal non-useraccessible hard drives, solid-state drives (SSDs), and the like (1247),may be connected through a system bus (1248). In some computer systems,the system bus (1248) can be accessible in the form of one or morephysical plugs to enable extensions by additional CPUs, GPU, and thelike. The peripheral devices can be attached either directly to thecore's system bus (1248), or through a peripheral bus (1249).Architectures for a peripheral bus include peripheral componentinterconnect (PCI), USB, and the like.

CPUs (1241), GPUs (1242), FPGAs (1243), and accelerators (1244) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1245) or RAM (1246). Transitional data can also be stored in RAM(1246), whereas permanent data can be stored for example, in theinternal mass storage (1247). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1241), GPU (1242), massstorage (1247), ROM (1245), RAM (1246), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of embodiments, or they can be of the kind well known andavailable to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1200), and specifically the core (1240) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1240) that are of non-transitorynature, such as core-internal mass storage (1247) or ROM (1245). Thesoftware implementing various embodiments can be stored in such devicesand executed by core (1240). A computer-readable medium can include oneor more memory devices or chips, according to particular needs. Thesoftware can cause the core (1240) and specifically the processorstherein (including CPU, GPU, FPGA, and the like) to execute particularprocesses or particular parts of particular processes described herein,including defining data structures stored in RAM (1246) and modifyingsuch data structures according to the processes defined by the software.In addition or as an alternative, the computer system can providefunctionality as a result of logic hardwired or otherwise embodied in acircuit (for example: accelerator (1244)), which can operate in place ofor together with software to execute particular processes or particularparts of particular processes described herein. Reference to softwarecan encompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. Embodiments encompass anysuitable combination of hardware and software.

FIG. 13 is a flowchart illustrating a method (1300) of decoding a codedpicture of a coded video sequence comprising a first segment and asecond segment, according to an embodiment. In some implementations, oneor more process blocks of FIG. 13 may be performed by the decoder (310).In some implementations, one or more process blocks of FIG. 13 may beperformed by another device or a group of devices separate from orincluding the decoder (310), such as the encoder (303).

Referring to FIG. 13, in a first block (1310), the method (1300)includes determining a first decoding process for decoding the firstsegment, in which a first prediction is disallowed, based on at least afirst syntax element of a high level syntax structure applicable to thefirst segment and the second segment, the first syntax elementindicating that the first prediction is disallowed.

In a second block (1320), the method (1300) includes determining asecond decoding process for decoding the second segment, in which asecond prediction different than the first prediction is disallowed,based on at least a second syntax element of the high level syntaxstructure, the second syntax element indicating that the secondprediction is disallowed.

In a third block (1330), the method (1300) includes decoding the firstsegment, based on the first decoding process in which the firstprediction is disallowed.

In a fourth block (1340), the method (1300) includes decoding the secondsegment, based on the second decoding process in which the secondprediction is disallowed.

At least one of the first segment and the second segment may include aslice.

At least one of the first segment and the second segment may include atile.

At least one of the first segment and the second segment may include agroup of blocks.

The first prediction may include one of an intra block copy acrosssegment boundaries, an intra prediction across segment boundaries, apredictive picture prediction across segment boundaries and abi-predictive picture prediction across segment boundaries, and thesecond prediction may include a different one of the intra block copyacross segment boundaries, the intra prediction across segmentboundaries, the predictive picture prediction across segment boundariesand the bi-predictive picture prediction across segment boundaries.

Each of the first syntax element and the second syntax element may be aflag of the high level syntax structure.

The high level syntax structure may be a segment header for each of thefirst segment and the second segment.

The high level syntax structure may be one of a picture parameter setand a sequence parameter set.

The high level syntax structure may be one of a picture header, a groupof blocks header and a sequence header.

Although FIG. 13 shows example blocks of the method (1300), in someimplementations, the method (1300) may include additional blocks, fewerblocks, different blocks, or differently arranged blocks than thosedepicted in FIG. 13. Additionally, or alternatively, two or more of theblocks of the method (1300) may be performed in parallel.

Further, the proposed methods may be implemented by processing circuitry(e.g., one or more processors or one or more integrated circuits). In anexample, the one or more processors execute a program that is stored ina non-transitory computer-readable medium to perform one or more of theproposed methods.

FIG. 14 is a simplified block diagram of an apparatus (1400) fordecoding a coded picture of a coded video sequence comprising a firstsegment and a second segment, according to an embodiment.

Referring to FIG. 14, the apparatus (1400) includes first determiningcode (1410), second determining code (1420), first decoding code (1430)and second decoding code (1440).

Referring to FIG. 14, the first determining code (1410) is configured todetermine a first decoding process for decoding the first segment, inwhich a first prediction is disallowed, based on at least a first syntaxelement of a high level syntax structure applicable to the first segmentand the second segment, the first syntax element indicating that thefirst prediction is disallowed.

The second determining code (1420) is configured to determine a seconddecoding process for decoding the second segment, in which a secondprediction different than the first prediction is disallowed, based onat least a second syntax element of the high level syntax structure, thesecond syntax element indicating that the second prediction isdisallowed.

The first decoding code (1430) is configured to decode the firstsegment, based on the first decoding process in which the firstprediction is disallowed.

The second decoding code (1440) is configured to decode the secondsegment, based on the second decoding process in which the secondprediction is disallowed.

At least one of the first segment and the second segment may include aslice.

At least one of the first segment and the second segment may include atile.

At least one of the first segment and the second segment may include agroup of blocks.

The first prediction may include one of an intra block copy acrosssegment boundaries, an intra prediction across segment boundaries, apredictive picture prediction across segment boundaries and abi-predictive picture prediction across segment boundaries, and thesecond prediction may include a different one of the intra block copyacross segment boundaries, the intra prediction across segmentboundaries, the predictive picture prediction across segment boundariesand the bi-predictive picture prediction across segment boundaries.

Each of the first syntax element and the second syntax element may be aflag of the high level syntax structure.

The high level syntax structure may be a segment header for each of thefirst segment and the second segment.

The high level syntax structure may be one of a picture parameter setand a sequence parameter set.

The high level syntax structure may be one of a picture header, a groupof blocks header and a sequence header.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media.

While this disclosure has described several embodiments, there arealterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

The invention claimed is:
 1. A method of decoding a coded picture of acoded video sequence comprising a first segment and a second segment,the method being performed by at least one processor and the methodcomprising: determining a first decoding process for decoding the firstsegment, in which a first prediction is disallowed, based on at least afirst syntax element indicating that the first prediction is disallowed;determining a second decoding process for decoding the second segment,in which a second prediction different than the first prediction isdisallowed, based on at least a second syntax element indicating thatthe second prediction is disallowed; decoding the first segment, basedon the first decoding process in which the first prediction isdisallowed; and decoding the second segment, based on the seconddecoding process in which the second prediction is disallowed.
 2. Themethod of claim 1, wherein at least one of the first segment and thesecond segment comprises a slice.
 3. The method of claim 1, wherein atleast one of the first segment and the second segment comprises a tile.4. The method of claim 1, wherein at least one of the first segment andthe second segment comprises a group of blocks.
 5. The method of claim1, wherein the first prediction comprises one of an intra block copyacross segment boundaries, an intra prediction across segmentboundaries, a predictive picture prediction across segment boundariesand a bi-predictive picture prediction across segment boundaries, andthe second prediction comprises a different one of the intra block copyacross segment boundaries, the intra prediction across segmentboundaries, the predictive picture prediction across segment boundariesand the bi-predictive picture prediction across segment boundaries. 6.The method of claim 1, wherein each of the first syntax element and thesecond syntax element is a flag.
 7. The method of claim 1, wherein thefirst syntax element and the second syntax element are of a segmentheader for each of the first segment and the second segment.
 8. Themethod of claim 1, wherein the first syntax element and the secondsyntax element are of one of a picture parameter set and a sequenceparameter set.
 9. The method of claim 1, wherein the first syntaxelement and the second syntax element are of one of a picture header, agroup of blocks header and a sequence header.
 10. An apparatus fordecoding a coded picture of a coded video sequence comprising a firstsegment and a second segment, the apparatus comprising: at least onememory configured to store computer program code; and at least oneprocessor configured to access the at least one memory and operateaccording to the computer program code, the computer program codecomprising: first determining code configured to cause the at least oneprocessor to determine a first decoding process for decoding the firstsegment, in which a first prediction is disallowed, based on at least afirst syntax element indicating that the first prediction is disallowed;second determining code configured to cause the at least one processorto determine a second decoding process for decoding the second segment,in which a second prediction different than the first prediction isdisallowed, based on at least a second syntax element indicating thatthe second prediction is disallowed; first decoding code configured tocause the at least one processor to decode the first segment, based onthe first decoding process in which the first prediction is disallowed;and second decoding code configured to cause the at least one processorto decode the second segment, based on the second decoding process inwhich the second prediction is disallowed.
 11. The apparatus of claim10, wherein at least one of the first segment and the second segmentcomprises a slice.
 12. The apparatus of claim 10, wherein at least oneof the first segment and the second segment comprises a tile.
 13. Theapparatus of claim 10, wherein at least one of the first segment and thesecond segment comprises a group of blocks.
 14. The apparatus of claim10, wherein the first prediction comprises one of an intra block copyacross segment boundaries, an intra prediction across segmentboundaries, a predictive picture prediction across segment boundariesand a bi-predictive picture prediction across segment boundaries, andthe second prediction comprises a different one of the intra block copyacross segment boundaries, the intra prediction across segmentboundaries, the predictive picture prediction across segment boundariesand the bi-predictive picture prediction across segment boundaries. 15.The apparatus of claim 10, wherein each of the first syntax element andthe second syntax element is a flag.
 16. The apparatus of claim 10,wherein the first syntax element and the second syntax element are of asegment header for each of the first segment and the second segment. 17.The apparatus of claim 10, wherein the first syntax element and thesecond syntax element are of one of a picture parameter set and asequence parameter set.
 18. The apparatus of claim 10, wherein the firstsyntax element and the second syntax element are of one of a pictureheader, a group of blocks header and a sequence header.
 19. Anon-transitory computer-readable storage medium storing a program fordecoding a coded picture of a coded video sequence comprising a firstsegment and a second segment, the program comprising instructions thatcause a processor to: determine a first decoding process for decodingthe first segment, in which a first prediction is disallowed, based onat least a first syntax element indicating that the first prediction isdisallowed; determine a second decoding process for decoding the secondsegment, in which a second prediction different than the firstprediction is disallowed, based on at least a second syntax elementindicating that the second prediction is disallowed; decode the firstsegment, based on the first decoding process in which the firstprediction is disallowed; and decode the second segment, based on thesecond decoding process in which the second prediction is disallowed.20. The non-transitory computer-readable storage medium of claim 19,wherein each of the first syntax element and the second syntax elementis a flag.